Approximation order of two-direction multiscaling functions

Orthogonal Two-Direction Wavelets of Order 2 From Orthogonal Symmetric/Antisymmetric Multiwavelets

“…The recursion coefficients p k are scalars. Two-direction scaling function ϕ and wavelet function ψ, which are a more general setting than the one-direction scaling function and wavelet, are investigated in [2,3,4,5,6,7].…”